Global Positioning System - About GPS

Figure 1: A GPS Satellite

The Global Positioning System (GPS) is a network of satellites that orbit the earth. "At any given time, there are 24 active satellites in the constellation. The constellation is composed of six orbital planes, each containing four satellites." (Dana, 2000)[See Figure 1]. GPS receivers can compute positions on the Earth using time and ephemeris (i.e. orbital position) information provided by the satellites.

GPS is ideal for demining, but it has many other applications. GPS revolutionized navigation and tracking. Whether it be by land, water, or air, GPS can be used to get just about anything from point A to point B. Various companies are using GPS to keep employees and products on track by mounting antennae on company vehicles. GPS is also used in missle guidance and for imagery correction through use of ground control points. Essentially, GPS applications possibilities are endless. GPS gives the users the ability to create, via these positions, their own custom data.  The data can later be used in a GIS to generate spatial data layers.

Three GPS Segments

Space segment: The network of satellites orbiting the Earth. These satellites have very accurate atomic clocks and broadcast radio signals to the Earth.

User segment: The users and their receivers. The receivers have less accurate clocks and use the signals sent by the satellite to calculate position.

Control segment: "Consists of five monitor stations (Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs), three ground antennas, (Ascension Island, Diego Garcia, Kwajalein), and a master control station (MCS) located at Schriever Air Force Base in Colorado that monitor the satellites." (Navstar, 1999)

There are three steps for utilizing GPS in mapping. Before the data is ever collected, planning must occur. After developing a data collection strategy, field data is then obtained. Finally, the data is processed and put into a useful form.

The International Mine Clearing Standards and Survey Types may be helpful in realizing the data collection needs.


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